1. Technical Field
The present invention relates to a liquid discharging apparatus, a head unit, an integrated circuit device for capacitive load driving, a capacitive load driving circuit, and a control method of a liquid discharging apparatus.
2. Related Art
In a liquid discharging apparatus, such as an ink jet printer, which discharges ink and prints an image or a document, an apparatus which uses a piezoelectric element (for example, a piezo element) has been known. The piezoelectric elements are provided corresponding to each of a plurality of nozzles in a head unit, and each of the piezoelectric elements is driven in accordance with driving signals. Accordingly, a predetermined amount of ink (liquid) is discharged from the nozzle at a predetermined timing, and a dot is formed. Since the piezoelectric element is a capacitive load, such as a capacitor, in terms of electricity, it is necessary to supply a sufficient amount of current in order to operate the piezoelectric elements of each nozzle.
For this reason, in the above-described liquid discharging apparatus, the piezoelectric elements are driven as a driving signal which is amplified by an amplifying circuit is supplied to a head unit (ink jet head). An example of the amplifying circuit includes a type which performs current amplification with respect to a source signal before the amplification by using a class-AB amplifier, but since energy efficiency is not excellent, in recent years, a type in which a class-D amplifier is used has been suggested (refer to JP-A-2013-146968).
The liquid discharging apparatus suggested in JP-A-2013-146968, the class-D amplifier for the ink jet head is driven based on a signal which is pulse-modulated in a self-excited oscillation type modulation method. In order to obtain (attain high accuracy of an output waveform) the discharge accuracy by the class-D amplifier for the ink jet head, high oscillation frequency (1 MHz to 8 MHz) which is 20 or more times higher than that of an audio class-D amplifier is necessary. However, due to the high oscillation frequency, the influence of various types of noise is likely to occur. For example, there is a possibility that malfunction of the class-D amplifier is generated due to the noise generated in a boosting circuit for the class-D amplifier, and thus, the discharge accuracy deteriorates. In order to prevent malfunction of the class-D amplifier due to noise, it is effective to synchronize a signal of a boosting clock of the boosting circuit with the modulation signal. However, the inventors have found that, in a case where the self-excited oscillation type class-D amplifier is used in reducing the size of the circuit scale for reducing the size of the liquid discharging apparatus, since the self-excited oscillation is not immediately started, there is a problem that boosting is stopped when performing of the synchronization is desired before the start of the self-excited oscillation. The driving voltage decreases due to the stop of the boosting, and the self-excited oscillation is stopped. Furthermore, the boosting of the boosting clock which is synchronized with the self-excited oscillation is not generated due to the stop of the self-excited oscillation, and it is not possible to avoid a dead lock state where both the boosting and the self-excited oscillation are not generated.